A new immunological reaction called cutaneous basophil hypersensitivity has recently been distinguished from classical tuberculin type delayed hypersensitivity. Recent work in our laboratory has shown that this delayed-in-time reaction featuring large accumulations of basophils, is transferable by either immune lymphocytes or immune serum. This research proposal submits a comprehensive program for the continued investigation of the immunochemical nature of the serum factors mediating cutaneous basophil responses. The basic hypothesis to be explored is that these are 7SIgG1 anaphylactic antibodies (or a subclass of this immunoglobulin type) with a relatively low affinity for antigen and binding properties of the Fc portion of the molecule through which cutaneous basophil responses are mediated. Experiments are also proposed which will follow up on our finding that thymic derived lymphocytes (i.e., T cells) can also transfer basophil reactions, and that basophil responses are suppressed in classical tuberculin hypersensitivity. The possibility that T cell transfers of basophil responses are dependent on contaminating donor B cells or similar potential antibody forming cells of recipients, will also be investigated. Finally, our encouraging initial demonstration of an anaphylactic function for basophils at cutaneous basophil reactions will be followed up, and our findings suggesting a critical T cell to mast cell to blood vessel requirement in delayed-type hypersensitivity will be investigated in depth.